Bill de Blasio visits the litter-and-needle-strewn stretch underneath railroad tracks in the Bronx.

Bronx Borough President Ruben Diaz Jr. is asking Mayor de Blasio to make the site of a Mott Haven homeless encampment populated by drug users into a new “Lowline” park.

Homeless people had set up on a litter-and-needle-strewn stretch of abandoned rail tracks underneath St. Ann’s Ave. at E. 150th St. But de Blasio paid a personal visit earlier this month — and a day later the eyesore was cleaned out by city workers.

“My office and all Bronxites are appreciative that this site, which had been home to a homeless encampment and was regularly used as a space for drug sales and abuse, has been cleaned up and its former occupants have been offered assistance,” Diaz wrote in a letter to the mayor, calling the camp “a considerable nuisance to the local community.”

But Diaz said the land should be developed instead of being left to sit — and called for a plan to build a “Lowline” park in the trench that holds the abandoned rail line, stretching 30 blocks from Mott Haven to Melrose and encompassing the site of the homeless encampment as well as other land.

“The best way forward on this site is not a temporary cleanup, but the development of a permanent use,” he wrote, saying the park “would be a model for the future reuse of the many miles of essentially abandoned railway that is spread across the five boroughs.”

“The best way forward on this site is not a temporary cleanup, but the development of a permanent use,” said Bronx Borough President Ruben Diaz Jr.

(Alec Tabak/for New York Daily News)

The land is owned by railroad company CSX and would have to be bought or seized by the city.

At street level above the rail tracks, Diaz proposed building housing. “There is a significant missed opportunity for housing along this rail right of way,” he said, noting the area’s zoning would allow new building.